Central Bureau for Astronomical Telegrams
IAUC 2787: A0535+26; 1975a
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Read IAUC 2788
Circular No. 2787
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Cable Address: SATELLITES, NEWYORK
Western Union: RAPID SATELLITE CAMBMASS
A0535+26
C. J. Eyles, G. K. Skinner and A. P. Willmore, University of
Birmingham; and F. D. Rosenberg, Mullard Space Science Laboratory,
report that the transient x-ray source A0535+26 has been found too
exhibit a strong periodicity. Observations by Ariel 5 Experiment A
on Apr. 28 indicated a modulation depth of greater than 25 percent
with a strong second harmonic component. The period is probably
104s.15 +/- 0s.20, although because of the long (32s) sampling time
periods of 46s.19 +/- 0s.04 or 24s.48 +/- 0s.01 cannot be excluded.
W. Mayer, Massachusetts Institute of Technology, reports that
the M.I.T. X-Ray Group has studied A0535+26 continuously for 3.0
days, from May 30.0 to June 2.0 UT, with the M.I.T. X-Ray
Observatory on the third Small Astronomy Satellite. The spectrum of the
source is extremely hard, and its intensity varies periodically
with a heliocentric period of 103s.8282 +/- 0s.0006 and an amplitude of
40-50 percent over the entire observed energy range of 1-50 keV.
Analysis of separate batches of data obtained during ten 95-min
intervals shows that the r.m.s. deviation of the phases of the minima
of the averaged light curves is less than 1s.0. Thus, if the object
is in an orbit with a period of between 3 hours and 6 days, then
a sin i < 6 x 10**10 cm. A strong first harmonic is present above 8
keV. At lower energies the first harmonic is nearly absent and
strong fourth and fifth harmonics are evident. On June 1 the
relative counting rates compared to the Crab Nebula were 0.2 and 0.5 in
the energy ranges 1-8 and 8-40 keV, respectively. These observations
were preceeded by the above report by Eyles et al.
L. A. Higgs, National Research Council of Canada, writes: "The
position of A0535+26 was scanned in R.A. and Decl. at a frequency of 10.6
GHz on May 19, using the Algonquin Radio Observatory 46-m antenna.
No radio source was seen in the 20' scans, with an upper limit of
50 mJy being established for any point radio source present.
PERIODIC COMET BOETHIN (1975a)
The following position was measured by C. McCarthy from an
exposure by E. Roemer and L. Vaughn with the Steward 229-cm reflector.
1975 UT R. A. (1950) Decl.
May 4.15625 6 48 02.56 +27 57 34.1
1975 June 2 (2787) Brian G. Marsden
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